This is a set of leg extensions for the Phantom 4. There is no need for zip ties or anything else. There are two sets. The shorter ones are extended by approx. 80mm. The longer approx. 110mm.
You must be careful when putting these on or removing them. As you know, the vertical part of the landing rails gets bigger as they go up. These are designed to go on the vertical shaft first, at the bottom of the shaft where it is smaller. Then push it up to cut on the horizontal skid part.
To remove, push down the vertical shaft (the horizontal part of the landing rail will pop off first), continue pushing down until the shaft is narrow enough to release the extension.
If you don't, you will almost certainly break them. But if they are put on and removed correctly, they do not break. That's just the nature of the axle.
It's a tight fit as they should be.